How often should you pressure wash a house in Miami's humidity?

In a dry climate you can wash a house every three or four years and get away with it. In Broward and Miami-Dade you cannot. Between 80 percent summer humidity, daily afternoon rain and salt in the air, organic growth on a wall starts within months of the last wash.

The short schedule

House walls, soft wash: every 12 to 18 months. Driveway and walkways: every 12 months, sooner on north-facing concrete. Roof, soft wash only: every 2 to 3 years, or the moment black streaks appear. Pool deck and patio: every 6 to 12 months, because bare feet and algae are a bad mix. Screen enclosure: every 12 months.

North-facing surfaces and anything under a tree canopy sit at the short end of every range. They stay damp longer, so growth gets a head start.

What you are actually removing

Those black streaks on a roof are gloeocapsa magma, a cyanobacteria that eats the limestone filler in shingles and tile. The green film on a north wall is algae. The dark speckles on concrete are mildew. None of it is dirt, which is why rain does not rinse it off and why a hardware store detergent does not touch it.

Pressure is the wrong tool for most of it

High pressure blasts the growth off the surface and leaves the roots behind, so it comes back faster each time. Worse, on tile roofs and painted stucco it strips material: cracked tiles, broken seals, and stripes in your paint that never go away.

Soft washing uses low pressure and a cleaning solution that kills the organism at the root. The surface comes out cleaner and stays clean two to three times longer. We use high pressure only where it belongs — concrete driveways, pavers and sidewalks.

Signs you are overdue

Black streaks running down from roof tiles toward the gutters. A green or gray tint on the north or east wall that a wet rag smears rather than lifts. A driveway that is two different colors where the car sits. Slippery patches on the pool deck after rain. Pavers looking dark in the joints.

The slippery pool deck is the one to stop ignoring. That is algae, and it puts people in urgent care.

What it costs

Our house soft wash runs about $0.35 per square foot with a $350 minimum. Driveways are about $0.25 per square foot with a $150 minimum. Roof soft wash is $0.60 per square foot with a $550 minimum. Most homeowners who stay on a yearly cycle spend less per visit than someone who waits four years and needs the heavier treatment.

Best time of year

Late fall through spring. Washing right after the rainy season ends removes a summer's worth of growth before it gets established, and the drier air means surfaces stay clean longer afterwards. If you can only do one exterior job a year, do it in November or December.

Send your address to 754-226-0066 and tell us which surfaces you are thinking about. We measure from aerial imagery for most homes and send a quote the same day. Serving Fort Lauderdale, Pembroke Pines, Weston, Sunrise, Davie, Miramar, Doral and the rest of Broward and Miami-Dade.